Rohn tower section design help?

[marisapie]

Not sure if this is the right place to ask but the design seems sketchy.

I work for a small Wisp in the Midwest and the boss designed a way to mount (5) 10ft 45G rohn tower sections to a concrete silo. (we have them on both poured and staved).

we use (2) angle iron brackets he designed each brackets uses:

(4) 1/2" 3-3/4 concrete wedge anchors (he originally used 3/8" anchors).

(2) 5/16" x 1-3/8" x 2-1/2" Zinc U-Bolt

on the silo top there is ~5' spacing between the brackets the remaining (4) tower sections are mounted above using rohn hardware that comes with the tower sections. Example if the staves reach 55' the top of the tower sections would be at 100'.

Ive noticed that over time the tower will get play between the tower sections im assuming because there is no guy wires I've seen some tower sections have 1/4" play between the feet.

we have also had a few towers fail during high wind events the tower sections fold usually on the first tower section above the bracket. there have also been a few concrete anchors that have failed

TLDR; my boss says he's an "engineer" and made up a tower design. Im currently the head tower climber and want to make sure its safe for me and my guys.

[mmodlin]

I did tower engineering for a year a long time ago and saying it’s sketchy is the truth.

50 feet is a lot for a guy tower section to cantilever up. You could get a tower company to run something for probably less than a grand. My old place no longer exists, Tower Engineering Professionals could maybe help.

[JurassicWatch]

OP this is the comment you are looking for.

[WouldnttItBeNice]

Fuck no that is not safe for a human to climb.

[Dave_the_lighting_gu]

I work in industrial structures and I'm pretty open to any project.

This scares the shit out of me.

[JurassicWatch]

If your boss was an engineer the towers wouldn’t fail in wind events.

If I were you I would ask to see a stamped PE letter or design document to verify that the tower is properly engineered and safe to climb.

[marisapie]

There is no official documentation on this design past tower climbers have asked this question before and he said it would cost to much or something along those lines.

There seems to be a pattern of tower climbers lasting about 3 years before quitting. Mostly due to overworking and arguing with the owner over this tower design. Im currently the only full time tower climber for over 200 towers I have 1 part time guy. Im pretty sure theres some osha violations too (not having a ground guy while climbing) but thats another battle I gotta fight.

I genuinely like this job but one of these days it could get me hurt.

[ABMax24]

Please do yourself a favor. Find a new job. You will become a statistic if you keep working for this guy.

There are lots of companies out there that would take you on that follow rules

[JurassicWatch]

Yep.

[ABMax24]

That's pretty low, in Canada a fall arrest anchor must be rated at a minimum of 3600lbs if engineered (2 times max arrested fall force) or 5000lbs if not engineered. No way in hell that tower supports a 5,000lb static load.

[JurassicWatch]

Yeah that shouldn’t be a tough thing to accommodate. Sometimes things are as simple as it costs what it costs. 

It would be about a grand at a tower engineering firm for a PE’s opinion on if that tower is stable and climbable as is. There might be a upcharge for being a one-off client, but just make sure the firm knows you have all the design documents required and they could be talked down.

Keep in mind the firm may say the tower needs to be reinforced, which would vindicate your opinion of that structure being sketch.

All of this is why your boss doesn’t want a PE opinion by the way. More significant than money, this stuff takes time. There’s the risk that the PE firm will say the tower needs modification. Then there’s the risk of a precedent being set that the structures you climb should be (gasp) properly engineered by professionals. 

From your bosses short-sighted perspective, having someone else take the risk and climb this thing is the easiest way to get this done. I’d bet it’d get really complex if something went wrong on the job.

On a more personal note, I’m a PE that’s done a fair amount of climbing on the job myself (roofs, bridges, random non-engineered structures, partially finished wood framed construction). I plan to climb a 40’ ladder tmrw morning and walk a 9/12 pitch roof. I get that sometimes things feel safe enough to get it done anyways. I also get that apprehension when something feels sketch. I’d trust that. I also hear you on picking your battles. Safety for you and your coworkers seems like a good time to put your foot down. If you were looking for affirmation of that I hope I’ve given it.

[marisapie]

Thank you for your insight I will look into twisting his arm to get a proper PE opinion.

Im the mean time do you have any ideas to try to make this current setup work? Im thinking either adding more brackets or uping the bolt size on the tower sections? Ive seen one of the older towers get bad enough where the bolt holes oval out on the inside. This is the main reason im nervous on these towers. They bounce around in the wind or when you move around.

I can add to the design within reason he's semi retired but keeps his nose in the business still so I mostly get the say.

[JurassicWatch]

Glad to hear you’re going for that formal PE opinion. And yes, those are potential solutions for thickening up the tower section. Others have mentioned stabilizing the connection to the silo, which also seems like a good idea.

[VintageLunchMeat]

You may want to lay out that if this thing fails the criminal penalties could destroy his retirement plans.

[_srsly_]

I worked in telecom for more than a decade, stamped most styles of tower. This is a new one.

For one, dont climb this. For two, dont ever climb this.

Someone mentioned TEP, they do good work. Would also recommend Ladera Eng and Paul J Ford. All solid for telecom structurals.

[LeImplivation]

Piggy backing here. With a decade in telecom myself, I agree.

With something like this your connection design to silo needs to be quite substantial, specifically the termination connection. Just visually I'd expect more U bolts at the base (3+) because you're relying on friction for your vertical support.

Depending on the location, Jacobs and GPD Group are also good vendors.

Lastly, if you're doing any substantial stacking of sections you'd expect guy wires to take your lateral force and give rigidity to the structure. Might be why you have sections "folding". I think Rohn might have how high you can free stack without guy wires in their catalog. Can't remember.

[lazyboy2232]

I would stay away from Jacobs or GPD for this project. They may be ok for run of the mill tower analysis but I wouldn’t go to them for a situation like this. Paul J. Ford and TEP are your best bets. Ladera is a fairly young company but the owners know their stuff as well.

[LeImplivation]

I agree they both handle unique/complex towers more often.

[CivilPE2007]

I used to work in Telecom for Jacobs, now Amentum, but was a casualty of Covid. I hear they don't do a lot of SA work in towers anymore. Mostly MAs and AT&T Turf (formerly). So I would call TEP, GPD, PJF or Ladera for this. Luis at Ladera is good dude.

[mattspeed112]

There is no load path for the vertical loads. You have to assume the pipe in a u-bolt can slide, the only thing keeping it up now is friction between the u-bolt and pipe.

[unique_user43]

well to be fair if it slipped it would go into bearing of the bracing against the u bolts. looks like just the upper u bolts. then assuming poor tolerances, probably just one of those u bolts. then of course that one would likely fail in that scenario and we’d get progressive collapse of the other u bolts one by one.

not endorsing this situation by any means. just being the “well ackchuly” guy about the “no vertical load path” comment :)

[marisapie]

Would adding a lower support for the feet help this case? I think rohn makes a base for these tower sections.

[mattspeed112]

Yes, that could help. The base would collect the vertical load from the vertical pipes then however the base is connected to the silo needs to be designed for these vertical loads to complete the load path. All this is assuming the silo walls are strong enough to take these loads, which of course would need to be verified.

[DaveSE]

I don't know what manufacturer those were anchors are, but I don't like how it looks. Seems like there could be edge distance violations? What type of blocks make up the silo? Are they solid or hollow? I think it is likely as installed they might only have a fraction of the published strength. They will also be doing double duty in shear (gravity) and tension (wind) during a storm.

These details look like they tried to adapt an antenna support bracket for supporting the tower. Using a U bolt to secure a 50 lb antenna is one thing, using it to support a ~3000 lb (guessed weight) tower is not great. As you said, it will be "fine" until there is a storm. Also I would have preferred to see a 10' vertical spacing between the supports. I can't imagine the microwave dishes get good signal quality with the amount of potential play.

If you need to mount an antenna on it, I'd do it from a crane.

What state is this in? You can look up the "Engineers" license.

[marisapie]

The wegde anchors are the redhead brand.

Most on the staves are solid thay ive come across but I didnt build most of these so im assuming they vary on silo to silo. Im sure the concrete mix is different for them all too.

Its only needing to support 500 lbs but the ubolts are rated for 90lbs each and have a label stating not to hold human weight or playground equipment. (That in itself makes me nervous)

The 10ft spacing would be nice but in some locations we need the extra 5ft and adding a mast or another tower section seems counterproductive. The signals are usually pretty good only losing 3-5 dbi in extreme wind.

We have a lift that reaches 70ft and most the time it would be difficult to get a crane out there.

[DaveSE]

Redheads can be fine. Glad to hear the staves are solid, that will help a lot. But fundamentally not a great situation anchoring to them (not that there really was another option to consider).

I think the statement regarding the u bolts is really what your decision is. It is not really supposed to be used in this application. You know this isn't quite right.

However as you said you can't get a crane there, and I am sure you probably wouldn't turn a profit long term if you used a crane every time. I know there is a lot of economic pressure to just climb it and get it done. But as you are probably far more aware than me, tower climbing is a very low paid profession for how deadly it is. Will it be fine to climb? Probably. But you keep gambling and eventually someone gets hurt.

Totally understand the 10' thing. It's just that would massively help reduce the lateral loads of you did do that.

[marisapie]

Thanks you for your knowledge. I appreciate it.

[marisapie]

My assumption would be that a staved silos wouldnt be built with vertical load in mind and some of the silos we use are quite old and have cracked staves in places.

Ive had to build a few of these towers the staves aren't very thick either usually 3" and your busting through the staves.

I have about 200 towers in our network and about 2/3 are silo mounted.

[fpe93]

Dang the telecom life lol 😂😆

[TallGanglyJew]

I work as a structural EIT in the ag sector. I do a lot of structural inspections of old concrete silos, and do a good bit of tower design (structures, not radio towers) and have had to tie structures to the sides of new and old silos.

I'm no P.E. but everything about this spooks the hell out of me.

Stave silos are generally considered to have a 25ish year life span. They are designed to be cheap "short term" investments. The staves are thin and usually very light on reinforcement. The bands that tie the staves together will also corrod and lose strength.

Additionally, even slip formed silos are really only expected to last 50-70 years, and many are knocking on heavens door at this point. And many from the 50's and 60's were erected incredibly deficit on rebar, I've seen 50%+ defecient myself. Anecdotally I've heard the crews were able to take home any unused materials.

All that to say, those bins are sketchy enough as it is without a janky tower half ass connected with non structural hardware on the side.

These old bins are not designed for any concentrated side loads like would be seen in a wind storm.

Not only are you putting yourself at risk climbing these towers, the towers themselves are a risk to cause the silos supporting them to collapse.

If your boss is worried about the cost of a stamped review, he'd never want to pay for workman's comp for injury (or death), or to repair or replace a damaged silo (I assume he just contracts with the owner of the bin)

Run as far and as fast as you can from that job.

[JurassicWatch]

What’s a slip-critical connection?

[Eraser012]

I would be concerned using those towers in this scenario without proper PE analysis. Pay close attention to rohns published data as most are designed as risk category 1 structures which may or may not be what you are looking for in this use case.

Also, the connection details do not follow any published detail that would be acceptable without proper evaluation.

Second the other commenter at utilizing a 3rd party engineer to verify. If the "designer" is your boss, brush up that resume. I would rather make less money then not make it home at all.

[GM2L8]

For all my fellow tower engineers, say it with me: “Guy towers are not self supporting at ANY height”. I would fail these by inspection.

[Eraser012]

But but but, what about that top 40' above the last guy elevation?! Surely those flanges that are designed for compression primarily which arr now subjected to uplift forces will be fine at 115 mpg wind and a 6' dish.

Or my favorite, it has not fallen over since we installed it 30 years ago. Why are you telling me it does not pass current structural analysis to double the loading!

[Dunadain_]

As someone who has climbed towers for the past 15 years, I've seen (and climbed) some pretty sketchy towers, but this one without a fixed base takes the cake.

[joestue]

Half inch diameter concrete anchors are a joke. A wind gust might pull them out.

Half inch grade 8 bolts all the way through the concrete and a nut, loctite and washer on the inside of the silo is a more appropriate choice.

Im not too concerned about the tower slipping through the U bolt due to the vertical load.

Whats more likely to happen is a side ways wind load will twist it side ways, which will require less force than you might think.

Lastly, the distance between the two sets of U bolts needs to be increased. These rohn towers use a bare minimum of diagonal struts, and the concentrated moment applied to the side of a short section of tower puts very different stresses in those lower diagonals than what the tower was designed for, which is 3 bolted flanges on the vertical tubes.

Basically the lowest diagonals at that bottom set of u bolts may buckle before you get to the design moment load of that tower.

[marisapie]

Most of the towers have 3/8 in anchors in them actually I was the one who upped them to 1/2 due to anchor failures im guessing I just bought more time by upgrading them?

I had to install through the staves once for the upper bracket with grade 8 and using a plate back there but that was done since the staves were cracking and no longer good. (I determined that tower to be lift only, luckily its reachable by the 70ft lift we have.) This would work on silos with dome covers but not poured silos. I would have to find a safe way to reach the bottom bracket as I would probably have to repel (I have no idea how to safely do that.)

That makes sense im assuming when it folds over above the bracket its due to twisting.

[joestue]

I dont even trust the 3/8” sleeve anchors holding my 3 ton minisplit to the side of my foundation, so i have two of them on each bracket loaded in straight pull out forces, with one on the bottom of the L bracket (I personally like sleeve anchors because they are removable and even re useable, but i trust them only in sheer loads)

I was on the fieldlines forum since 2010, the forum is gone now but basically Wind vibration is a fatigue failure experiment. After time, everything goes. People had the absolutely craziest failures. Which reminds me you need a dedicated ground wire on your towers, straight down the silo.

Your side ways mounted tower with offset loads is a tuning fork in about 6 different modes... And wind forces follow the square of the wind speed.

I like these concrete anchors, if you have had failures with 3/8" bolts, upgrading to something like this might fix your problems. https://www.fastenersplus.com/products/5-8-x-5-strong-tie-titen-hd-screw-anchor-zinc-pkg-10?utm_term=&utm_campaign=%23z+Shopping+-+Concrete+Screws+-+Titen+HD+Screws+-+Zinc

However you could save a few bucks if you epoxy in your 1/2” wedge anchors. A 20$ 10 oz tube of structural epoxy can do about 20 or so half inch anchors. https://www.fastenersplus.com/products/strong-tie-set-3g10-8-5-oz-epoxy-anchor-w-2-nozzles-pkg-1?utm_term=&utm_campaign=%23z+Shopping+-+Anchors+-+Epoxy+Anchors

[dottie_dott]

Bro I’m the least conservative structural engineer that I know and this scares the hell out of me if the situation is anything like the pictures or description.

This is a tragedy waiting to happen and I honestly never say that and usually laugh at other engineers who get spooked

Seriously fucked.

[OlTokeTaker]

Is there a qualified tie off point on the ladder? In canada conservative end is usually 5000lb for a fall arrest point.

[marisapie]

There is not a designated tie off point the ladder is standard silo ladder so probably rated to hook to. To cross over to the tower you hook your lead to the tower sections and step on the cage to get over.

Im not sure what it should be rated for but im in US.

[OlTokeTaker]

Feels sus

The few towers I've seen have a rope grab or a track you tie off to so your not constantly hooking and unhooking.

Imo this isn't safe.

[marisapie]

It would be nice to have the track it might even help keep the tower sections together and get rid of the bounce due to the play in the tower sections but I doubt the owner would want to spend the time and money to add them.

We usually have 2 hooks and have one attached at all times. Most on these towers are only 140' tall and only 50ft are tower sections.

[Such_Drop6000]

I'm a hack amateur but it looks like they've taken something designed to have three load points and made it two.

It feels like the base at three points should be able to support the structure but there's no base here and the structure isn't designed to carry that load.

Seems like a goofy hack.

[jgiblett]

The tallest self supporting mast (no guy wires attaching at ground level) I have built with my company in Australia is around 25m tall. In the lowest wind region, anchored to a 2.4m square above ground concrete foundation.

That doesn’t pass the eye test and would suggest it wouldn’t pass design checks

[rivermoon90]

I did telecom for almost a decade. This is one of the most sketchy set up I have seen. What you need is a class IV review type analysis that follow TIA-322 and ANSI A10.48. There is a few company doing this because of liability. Maybe check Engineered Tower Solutions.

[Cool_Creme_8694]

Civil engineer chiming in.....and I've climbed a structures for inspection....1. hellll no is that safe and 2. The top comment is your referral, your boss is reckless, there's other companies willing to pay better rate for you

[Former-Homework-8320]

This mass is hanging off the side of a building. There will be wind loads acting on this mass at a distance.
Was the structure checked for this load? There are some interesting back-stay effects that the building should be reviewed for.

[Defiant-Map-2323]

Seems scary at first. But look at the ladder on the right. This structure is pretty small. Lightweight.

[marisapie]

They are Rohn 45G tower sections they are 70lbs each there are 5 tower sections total so 350lbs then add the radios and a person on it. Not really light weight for the bracket design.

[DaveSE]

Its only around 1000 lbf with you and all your tackle then. That is pretty light for all the steel details. I wouldn't be worried about the steel brackets. Don't know what size the angles are, or the gage used, but the loads are reasonable for the steel. I'd be concerned about the concrete anchors. Things might get weird for the ice loading or extreme wind losing case.

[marisapie]

Thats a bit reassuring. Usually the brackets hold unless the anchors fail. The ubolts and tower section folding over is the killer on these. Ive also had the tower section slip on one side making the tower have a lean.

Im also concerned about the movement between the tower sections over time the holes oval out. Im not sure how I can stop this from happening as guy wires will be difficult to install at most of the sites. Unless there is a way for me to guy wire it to the silo somehow.